The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 10-13431 filed Jan. 7, 1998.
1. Field of the Invention
The present invention relates to an exposure method and a scanning-type exposure apparatus utilized in a photolithography process implemented to manufacture semiconductor devices, liquid crystal display devices, thin-film magnetic heads or the like, and more specifically, it relates to an exposure method and a scanning-type exposure apparatus that are ideal in application for exposing a substrate that has become deformed during the manufacturing process.
2. Related Art
The use of liquid crystal display devices as display elements in personal computers, television sets and the like has become increasingly extensive in recent years. Such a liquid crystal display device is manufactured by laminating a plurality of pattern layers constituting transparent electrode layers and switching elements on a glass substrate. These pattern layers are patterned through photolithography. During the photolithography process implemented to manufacture a liquid crystal display device, a projection exposure apparatus that projects an image of an original pattern formed on a mask onto the glass substrate via a projection optical system and transfers the pattern onto the glass substrate by photosensitizing a photoresist layer applied on the glass substrate, for instance, is utilized.
An example of such a projection exposure apparatus is now explained in reference to FIGS. 12 and 13, which illustrate a scanning-type exposure apparatus that performs exposure processing on a glass substrate (plate). FIG. 12 is a perspective illustrating a schematic structure of a scanning-type exposure apparatus in the prior art. FIG. 13 illustrates an alignment operation performed to align the mask and the plate in the scanning-type exposure apparatus in the prior art shown in FIG. 12.
In FIG. 12, a plate 22 is held at one sidewall of a carriage 21 having its cross section formed in a U shape and a mask 23 is held at the other sidewall. The pattern in a partial area of the mask 23 held by the carriage 21 is illuminated by exposing light irradiated from an illumination system 24 and as the exposing light having been transmitted through the mask 23 is transmitted through a projection optical system 25, the pattern at the partial area of the mask 23 is transferred onto an area on the plate 22. During such an operation, the carriage 21 is caused to travel over a guide 20 in a specific direction A (the scanning direction) so that the pattern in the entire area on the mask 23 is transferred onto the plate 22.
During the exposure operation described above, the projected image of the pattern formed at the mask 23 and the pattern layer that is already formed on the plate 22 must be accurately aligned with each other. Accordingly, an alignment operation is performed to align the mask 23 and the plate 22.
In order to implement this alignment operation, alignment marks formed on the mask 23 and alignment marks formed on the plate 22 are observed with alignment microscopes 26 and 27 to correct the positional relationship between the mask 23 and the plate 22 by detecting any positional misalignment between them. The plate 22 and the mask 23 are each provided with a plurality of alignment marks formed at the two ends along direction Y, which are formed to extend along direction X, and one or a plurality of these alignment marks are observed through the alignment microscope 26 or 27. Based upon the results of detections performed by using the alignment microscopes 26 and 27, the position of the plate 22 relative to the mask 23, the size of the plate 22 relative to the mask 23 and the like are ascertained, and using such information, the position of the mask 23 is adjusted or the magnification power of the projection optical system 25 is corrected.
For instance, if it is detected through the alignment microscopes 26 and 27 mentioned above that the plate 22 and the mask 23 are offset from each other in parallel along direction X and direction Y, as illustrated in FIG. 13(a), the mask 23 is caused to move in parallel over a specific distance by driving an actuator 28 that moves a mask table 32 holding the mask 23 along direction X and driving two actuators 29 and 30 that move the mask table 32 along direction Y (shift correction).
In addition, if there is a rotational misalignment between the plate 22 and the mask 23 around the Z axis, as illustrated in FIG. 13(b), the mask 23 is caused to rotate by a specific quantity by varying the degrees to which the actuators 29 and 30 are driven (rotation correction). If the sizes of the mask 23 and the plate 22 do not match relative to each other, as illustrated in FIG. 13(c), the magnification power of the projection optical system 25 is corrected along direction Y and the magnification power along direction X is corrected by driving the actuator 28 along direction X to move the mask 23 indirection X while the carriage 21 is engaged in a scanning movement and change the relative scanning speed of the mask 23 and the plate 22 by a specific degree (scaling correction).
In more specific terms, if the plate 22 extends along direction X by 4 ppm, for instance, the actuator 28 must be driven to move the mask 23 by 4 ppm in the opposite direction from the scanning direction as the carriage 21 engages in a scanning operation.
It is to be noted that the alignment marks at the mask 23 are formed in advance when the mask is formed, whereas the alignment marks at the plate 22 are normally formed during the initial exposure processing.
A plate that is delivered to a projection exposure apparatus to be exposed usually undergoes a plurality of heat treatments during the process and undergoes repeated exposure of the original pattern over a plurality of layers. Expansion or contraction of the plate mainly attributable to the heat treatments implemented in the process may result in deformation of the plate. For instance, after the plate undergoes various process, a plate having a rectangular planar shape with individual sides each extending almost linearly, as illustrated in FIG. 14(a), may become warped with a curvature along direction Y as illustrated in FIG. 14(b) or become deformed into a parallelogram shape, as illustrated in FIG. 14(c).
When exposing a plate that has become deformed, as illustrated in FIG. 14(b) or FIG. 14(c), the degree of deformation along direction Y successively changes as it travels along direction X for scanning during an exposure operation, and this poses a problem in that full alignment correction cannot be achieved through the shift correction, the rotation correction or the scaling correction in the prior art. A pattern that is exposed without an accurate alignment manifests a significant alignment overlay error relative to the base pattern, which results in a problem in that the characteristics of numerous elements formed on the plate become inconsistent among the individual areas of the plate.
An object of the present invention is to provide an exposure method and a scanning-type exposure apparatus that achieve accurate alignment for a deformed substrate.
The object described above is achieved with an exposure method for exposing a substrate with a pattern formed on a mask by synchronously moving the mask and the substrate, comprising a step in which any change in the shape of the substrate is detected and a step in which the relative positions of the mask and the substrate are corrected during the synchronous movements based upon the results of the detection results.
In addition, in the exposure method according to the present invention, the pattern on the mask may be projected onto the substrate by a projection optical system. Also, in the correction step, the mask may be moved in a direction roughly perpendicular to the direction of the synchronous movements and the direction of the optical axis of the projection optical system.
In the exposure method according to the present invention, any change in the shape of the substrate may be detected based upon a state of alignment of at least three alignment marks provided along the direction of the synchronous movements of the mask and the substrate in the step for detecting change in the shape of the substrate, and the results of the detection may be approximated to functions represented by at least two straight lines or curves to correct the relative positions based upon the functions.
In addition, the object described above is achieved in a scanning-type exposure apparatus that exposes a substrate with a pattern formed on a mask by synchronously moving the mask and the substrate, comprising detection devices that detect any change in the shape of the substrate and correction mechanisms that correct the relative positions of the mask and the substrate during the synchronous movements based upon the results of the detection.
The scanning-type exposure apparatus according to the present invention may be further provided with projection optical systems that projects the pattern of the mask onto the substrate. Furthermore, in the scanning-type exposure apparatus according to the present invention, the projection optical system may be provided with a plurality of erect non-reverse image projection lenses. In the scanning-type projection apparatus according to the present invention, which is further provided with a magnification power adjustment mechanism that adjusts the projection magnification power of the projection optical systems, the correction mechanism may control the magnification power adjustment mechanisms based upon the results of the detection. Moreover, the scanning-type exposure apparatus according to the present invention may be provided with a positional adjustment mechanism that adjusts the position of the pattern projected onto the substrate by the projection optical system. By utilizing the magnification power adjustment mechanism and the positional adjustment mechanism in combination, any deformation occurring at the substrate can be dealt with so that the pattern on the mask is accurately transferred onto the substrate.
In addition, the exposure method according to the present invention described above includes a step in which the projection magnification power of the projection optical system is adjusted during the synchronous movements. Also, in the exposure method according to the present invention, the projection optical system comprises a plurality of erect non-reverse image type projection lenses and portions of projection areas of the plurality of projection lenses overlap to be exposed each other, so that above-noted exposure is performed.
In addition, the exposure method according to the present invention described above includes a step in which the position of the pattern projected onto the substrate by the projection optical system is adjusted during the synchronous movements. In this exposure method, the mask is moved along a direction substantially perpendicular to the direction of the synchronous movements and the direction of the optical axis of the projection optical system in the correction step. Furthermore, the exposure method includes a step in which the projection magnification power of the projection optical system is corrected during the synchronous movements.
Moreover, in the scanning-type exposure apparatus according to the present invention described above, the correction mechanism drives a mask stage holding the mask along a direction substantially perpendicular to the direction of the synchronous movements and the direction in which the optical axis of the projection optical system extends.